1. Field of the Invention
This invention relates to integrated circuit (IC) chips the circuitry of which is controllably switchable to a low-power-consumption non-operating status to conserve power, as for use in battery-operated apparatus and the like. More particularly, this invention relates to an IC chip having an analog-to-digital converter which is controllably switchable between a normal mode and a low-power-consumption mode wherein the power consumption is drastically curtailed during times between conversion operations.
2. Description of the Prior Art
The growth in use of battery-operated equipment, such as lap-top computers, has sharply increased the need to reduce power consumption in the integrated-circuit devices employed in such equipment. Various ways of reducing the power consumption have been developed. One important technique has been that of supplying full-power to the device only during short periods of normal operation, and placing the device in inactive mode (sometimes called "power down" or "sleep mode") during intervening non-operating periods. For example, in an integrated-circuit chip having a number of transistors for amplifiers, converters, or other function elements, the transistor bias voltages can be switched by a control signal to levels precluding normal operating current flows, thereby reducing the power drain by a factor of 100 or even 1000 to one.
Although such power-reducing circuitry has come into considerable use for A/D converters, there has remained a problem of how best to develop the control signal for switchover between normal power mode and low-power mode. If the chip is switched from low-power mode to normal power mode every time a conversion operation is carried out, the time required to carry out a conversion operation will increase significantly since the power to the converter circuitry must first be brought back up to operational levels prior to performing the conversion. Thus, it is desirable to allow the user to choose whether the IC chip should automatically switch to low- power mode after each period of operation, or whether the part should remain in full-power mode at all times in order to ensure fastest overall operational speed. In addition, controlling the switchover between normal mode (continuous full power) and low-power mode (intermittent full-power operation) advantageously should be effected by means which do not require an additional pin on the IC part, or adding to the bits in the control register for the part. Moreover, the apparatus for effecting this switchover should be reliable in operation yet modest in additional cost.